The objectives of the research to be carried out under this grant are: 1. establish monolayer cultures containing adrenal chromaffin cells obtained from neonatal rat adrenal medullae or pheochromocytes obtained from a transplantable rat pheochromocytoma; 2. utilize an established selection technique to isolate from these cultures cell lines which contain tyrosine hydroxylase activity, and subsequently use conventional procedures to isolate defined clones of each cell tyep; 3. compare levels and cellular distribution of catecholamines and catecholamine synthesizing enzymes of the cultured cells with those of the tissues from which they were derived, using a combination of biochemical assays and histochemical localization techniques at the light and electron microscope levels; 4. examine the secretory responses of the cultured cells to acetylcholine, other secretagogues, and an altered ionic environment on both biochemical and morphological bases; 5. use this in vitro model to investigate the fate of the adrenal chromaffin vesicle after it has released its secretory products by exocytosis.